Question

The formation of glucose-1-phosphate from glucose and orthophosphate has a G of + 20.9 kJ/mol. If this reaction were coupled to another reaction in order to produce an exergonic reaction, which of the following would produce an overall endergonic reaction and therefore not be suitable for coupling?

A) creatine phosphate + H2O  creatine + Pi

B) AMP + H2O  adenosine + Pi

C) ATP + H2O  AMP + PPi

D) ATP + H2O  ADP + Pi

E) 1,3-bisphosphoglycerate + H2O  3-phosphoglycerate + Pi

Answer 1

Exergonic reaction : Negative free energy change

Endergonic reaction: Positive free energy change

The standard free energy change for the given reaction is 20.9 kJ/mol. So for producing an overall endergonic reaction we need to couple with the reaction for which the standard free energy change is greater than -20.9 kJ/mol. The free energy change for the given reactions are as follows,

A) -43 kJ/mol

B) -14 kJ/mol

C) -31 kJ/mol

D) -31 kJ/mol

E) -49 kJ/mol

Therefore equation B is not suitable for coupling.